Push-through packaging, also referred to as blister packaging, has applications in a variety of industries including the food and medical markets. But it is in the pharmaceutical area where metered provision to patients of ampules, tablets or capsules to patients provided in blister packs occurs that it has found its broadest application in the past. This type of packaging typically consists of a top lid stock, or lidding, applied to a thermoformed bottom often made from a polyvinyl chloride (PVC). Blister packages used in the pharmaceutical industry have particularly demanding requisites which the packaging industry has found difficult to meet concurrently in a single product formulation. These include the need to prevent package curling so that high volume cartoning can be accomplished faster and more easily and storage problems are minimized; the provision of simultaneous easy printability, sealability and machinability; the production of an effective, recyclable barrier for preventing moisture transmission; the facile disposition of trim from the product during manufacturing and after use through recycling and, finally, the attainment of a thin gauge material with the proper, desirable level of brittleness of the push-through lidding so that the physical effort required to access the packaged product is neither too great for the elderly nor too easy for children. In addition, the package must have a cosmetically pleasing appearance to consumers. Prior art packaging has experienced problems in meeting one or more of the recited goals due primarily to the composition of the lidding used for the particular package.
A widely used type of lidding relies on a metallic foil lid stock, often with an aluminum component. Such foils can provide an adequate moisture vapor barrier, a thin gauge material, eventual printability and the desirable push-through characteristics. However, such lidding also has the disadvantages of high cost, the necessity of treatment or surface coating to achieve printability, difficulties in recycling the entire package after use and curling of finished packages.
Another type of lidding is made from polyamide or polyethylene. Although such lid stock solves many of the problems listed above, its primary disadvantage is the difficulty encountered in recycling packages in which it is used.
A third choice involves blister packs with bottoms made from polyvinyl chloride (PVC) or polyethylene terephthalate and lidding composed of paper or card stock. Recycling such packages is complicated both by the absence of a satisfactory method of separating the lidding from the front blister and the tendency of fibers from the lidding to adhere partially to the front blister during removal.
Still another possibility has been the use of polypropylene lidding. Such packages are subject to curling, are difficult to work with and do not store well.
There exists, therefore, a need for a lid stock material which is completely recyclable with a PVC bottom both during manufacture and after use, cost effective, directly printable and curl resistant while retaining desirable push-through and moisture vapor characteristics in a thin gauge material.